To some degree, Saturns moon Titan, with its low gravity, thick
atmosphere and exotic surface composition, hardly resembles Earth. Despite
such differences, however, new images from NASAs Cassini spacecraft
are revealing that some physical surface processes behave in much the
same way on both Titan and Earth. The new images show regions of Titan
with vast systems of 100-meter-tall linear dunes, similar in shape and
size to formations seen in Earths Namib and Sahara deserts, and
are helping researchers understand Titans wind patterns.

Some astronomers once thought that the dark regions seen in initial Titan
images were possible sites of liquid methane oceans. But radar images
of Titan returned from the Cassini orbiter on Oct. 27 revealed that instead
of methane oceans, some of the dark spots are actually dunes, according
to Ralph Lorenz, an astronomer at the University of Arizona in Tucson.
The discovery rules out the possibility of surface liquid at dune locations
 as in the arid deserts on Earth, liquid would prevent dune movement
and growth.

Dune systems cover 65 percent of the October flybys imaged path,
with some systems spanning areas 1,500 kilometers by 200 kilometers, says
Lorenz, who, with colleagues, published the details in the May 5 Science.
The structures form from sand-sized grains, but instead of Earth-like
sand, Titans grains are possibly composed of ice or organic materials.
Despite differences in composition from Earth dunes, the morphological
result is the same, Lorenz says.

Beyond studying dune characteristics, Lorenz used the dunes to map Titans
winds. Surface winds on Earth derive much of their energy from the sun,
and astronomers once thought Titan orbited too far from the sun to maintain
surface winds strong enough to sculpt dunes. But it turns out that gravitational
tugs from nearby moons and planets do the trick. Saturns pull on
Titan creates winds strong enough to sculpt the observed features, Lorenz
says. Also, the various orientations of Titans dunes, which stretch
lengthwise in the same direction as the wind, indicate that surface winds
are shifty. Such information helps provide the big picture
of a really interesting place, he says.

Lorenz says that he will not be surprised if future Cassini flybys turn
up more dune patches on other parts of the moon. In the meantime, he says,
astronomers are considering ways to take a closer look at Titans
dunes and other surface features by means of an airship or altitude-controlled
balloon.